Video Transcript (English)

Hello there! In this video, you’ll learn how to use comparison operators in MongoDB. We’ll work with the following operators: $gt (greater than), $lt (less than), $lte (less than or equal to), and $gte (greater than or equal to).

The names of comparison operators follow a pattern, so they’re easy to remember. Note that each operator starts with a $ to distinguish it from a field.

To use a comparison operator, we specify a field followed by the comparison operator and a value.

Let’s go over each of the comparison operators to get a better idea of how they work.

We’ll start with $gt, the “greater than” operator. It returns documents where the field contains a value greater than the specified value.

Let’s examine the following document, which contains an items field that’s an array of sub-documents. The items field contains various fields for each item, including the price, which is what we’re interested in.

We access sub-documents by using dot notation.

In this expression, we want to find every document with at least one item price greater than $50.

To access sub-documents, we must first specify the document field name, followed by the name of the sub-document field name in quotes. In this case, it’s the items.price field. 

When we run this command, all the results contain at least one item sub-document with a price greater than $50.

We can also easily find items with a price less than $50 by changing a single letter in our expression, from $gt to $lt.

The expression now returns every document that contains an item sub-document with a price less than $50.

Next, let’s look at $lte, the “less than or equal to” operator. It works like the “less than” operator, except that it returns all documents less than or EQUAL to a given number.

In this expression, we’re searching for every document in the sales collection containing a customer whose age is less than or equal to 65.

After we run this command, all the results will contain a customer who is 65 years or younger.

While we’re at it, let’s take a quick look at the “greater than or equal to” operator. We just need to update the $lte operator to $gte.

The expression now returns every document with a customer whose age is 65 years or older.

Awesome job! You now have a basic understanding of how to implement comparison operators in your queries.

Here are the operators we covered: $gt (greater than), $lt (less than), $lte (less than or equal to), and $gte (greater than or equal to).

MongoDB isn’t limited to the comparison operators covered in this video. We have a wide range of comparison operators to choose from. Check out our documentation to experiment with some of the other operators MongoDB supports.